Biomedical Engineering Reference
In-Depth Information
materials offer versatility in designing an exogenous ECM with spe-
cificpropertiessuchasporosityandmechanicalstrengththatcanbe
manufactured reproducibly on a large scale.
Among the available candidate biomaterials, extensive research
concentrates on PLGA, a synthetic-type material classified under
hydrolytically degradable polymers. PLGA undergoes bulk erosion
through hydrolysis of the ester bonds with the rate of degradation
that depends on a variety of parameters, including the lactic and
glycolic acids ratio and the molecular weight, shape, and structure
of the matrix. 52 The major popularity of PLGA is attributed in part
to its approval by the Food and Drug Administration (FDA) for use
in humans, its good processibility, which enables fabrication of a
variety of structures and forms, and controllable degradation rates.
Besides, PLGA demonstrates good cell adhesion and proliferation,
makingitapotentialcandidatefortissueengineeringapplications. 53
Under such considerations, the use of PLGA is also one of the ideal
choices as the main matrix for the shell of ORMs. In this case, PLGA
isinerttowardsH 2 O 2 andcanbeeasilyfabricatedintomicron-sized
particles having H 2 O 2 encapsulated. PLGA plays a role in shielding
theH 2 O 2 frombeingdecomposedbypossiblecatalystsfromthesur-
roundings, while at the same time becoming the barrier to avoid
harmful direct contact of the free H 2 O 2 with cells. Slow release of
the H 2 O 2 gives su cient time for its complete decomposition into
oxygen.
Sometimes the issue of incompatibility of physical properties
betweeningredientsusedinproducingORMsarisesunderunavoid-
able circumstances. As a consequence, the microsphere loses the
smart capability in creating an optimum level of oxygen for cell sur-
vival.ThisissuealsoexistsinthesystemofusingH 2 O 2 encapsulated
in PLGA for oxygen generation, where two main ingredients cho-
sen have different physical properties. PLGA is highly hydrophobic,
while H 2 O 2 is highly hydrophilic. Thus the possibility of incomplete
H 2 O 2 encapsulation may occur due to the strong expel force gener-
ated during the meta stable stage of the synthesis, a stage when all
ingredientsarestillintheliquidphasewithhighmobility.Phasesep-
arationcaneasilyoccur,failingtheincorporationofH 2 O 2 withinthe
solidifiedPLGAmicrosphere.Toovercomesuchaproblem,twopos-
siblestepscanbeemployed—creatingbettercompatibilitybetween
ingredients and modifying the preparation methodology that can
 
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